Fibre Channel (FC) is a computer communications technology supporting fast data signal transmission, e.g., up to 4 gigabit-speed, used, for example, for storage networking. FC disk drives may be used in disk array enclosures (DAE) on storage systems, such as storage systems produced by EMC Corporation of Hopkinton, Mass. (See, for example, “EMC 2-Gigabit Disk-Array Enclosures (DAE2) FC and ATA Models,” HARDWARE REFERENCE, P/N 014003048, REV A02, published February 2003 by EMC Corporation, which is incorporated herein by reference.) Backend DAEs of the storage system may connect to a host central processing unit (CPU) through an FC protocol card. (See, for example, U.S. Patent App. Pub. No. 2004/0193791 to Felton, et al., and U.S. Pat. No. 6,574,687 to Teachout, et al., which are both incorporated herein by reference). Other types of disk enclosures may also use FC disk drives and may operate with the system described herein. For example, disk processor enclosures (DPEs) may be used that include FC disk drives and storage processors.
While data read/written to a DAE is communicated using FC protocol, there is also a need to communicate DAE management information to the DAE logic, such as Enclosure Services information. Due to the large number of disk drives that may be connected, in EMC storage systems diplexing is used on FC signals, where out-of-band management signaling is combined with in-band FC data traffic on the FC interconnect in order to facilitate DAE management. Diplexing in storage systems involves driving both positive and negative FC differential signals with a common-mode out of band signal. (See, for example, U.S. Pat. No. 5,901,151 to Bleiweiss, et al., which is incorporated herein by reference.) The imposed common-mode signal may carry an RS232 data stream containing DAE management information. Differential receivers at the end of the line will ignore the imposed common-mode signal as common-mode noise; while a simple filter may be used to extract the RS232 signals.
On some EMC Corporation FC protocol card designs, a universal asynchronous receiver/transmitter (UART) switch may be used to connect multiple downstream diplexed circuits from DAEs to the upstream storage processor (SP) UART input/output. Each SP in an EMC system may have multiple FC protocol cards and each protocol card may include multiple FC ports connected to the DAEs.
COM ports (e.g., an RS232 serial port, such as used with an UART) are considered legacy hardware and are being replaced in the industry with universal serial bus (USB) interconnects. It is common for processor and operating system (OS) vendors to make their latest products offerings “legacy free.” For example, processor vendors either do not have COM ports in their latest product offerings, or the number of available COM ports is limited. OS vendors may restrict the use of COM ports in a legacy-only environment, where most of the interrupts needed to handle UART traffic are reserved for a wide variety of legacy peripherals. Further, even if the legacy hardware features are missing, it may be that the reserved interrupts cannot be re-configured to support other hardware. With the limited amount of UART resources available, both in hardware and OS, the number of protocol cards that may be supported in a storage system is becoming increasingly limited.
Accordingly, it would be desirable to provide a system that allows connections between incompatible ports among newer and older versions of products, such as USB and RS232 serial ports, to be made efficiently and without incurring extensive costs as may be required for hardware or other system design changes.